I have a pretty high maximum heart rate of 194 (I'm 50). What I've noticed is that, in comparison with training colleagues, I tend to spend more time in the "Threshold zone" in Strava (169-188 bpm), even in efforts where I feel comfortable and they complain. While I know that max heart rate is different from person to person and unrelated to fitness level, my question is if and how much different individuals have different profiles in terms of how much time a) they spend close to their max heart rate and b) they are able to sustain it. (in other words, is it a indicator of over-training or it depends on the person).